1. Field of the Invention
The present invention relates to a technology for creating an interpolation frame between reference frames.
2. Description of the Related Art
In general, there are two types of display devices, namely, an impulse-type display device and a hold-type display device. The impulse-type display device emits light only for a certain persistence period of phosphor after writing an image onto a screen of the display device. A cathode ray tube (CRT) display and a field emission display (FED) are categorized as the impulse system, for example. The hold-type display device holds display of a last image frame until a new image frame is written. A liquid crystal display (LCD) and an electro-luminescence display (ELD) are categorized as the hold type, for example.
One of drawbacks of the hold-type display device is a blur event that occurs while displaying a moving image. The blur event occurs because images of a plurality of frames are superposed and reflected in eyes when a moving object appears in the images across the frames and the eyes of an observer follow the movement of the moving object.
Despite that the same image of the previous frame is kept being displayed until the previous frame of the displayed image is replaced with the next frame, the eyes observe the moving object by moving their sight to the moving direction of the moving object on the previous frame while predicting display of the next frame of the image. In other words, following movement of the eyes is continuous, and the eyes perform sampling of the image at intervals shorter than an inter-frame spacing of the moving image. As a result, the eyes visually recognize an image between two successive frames to compensate the spacing, thereby observing the blur event.
The problem can be solved by setting a shorter inter-frame spacing for displaying. This can also improve unnatural motion in a moving image with a few display frames. One of conceivable concrete approaches is to create an interpolation image by using motion compensation, which is used for an MPEG2, to interpolate between successive frames.
The motion compensation uses a motion vector detected by block matching. However, MPEG2 creates an image block by block, so that if a block includes a plurality of objects that moves differently, correlated part and uncorrelated part arise within the block, thereby resulting in block distortion due to the uncorrelated part.
JP-A 2004-104656 (KOKAI) discloses a method of interpolation frames for solving these problems. A block is divided into a plurality of areas, and a motion vector is obtained per each area. This can reduce block distortion in a block that includes objects with different motions. Moreover, an optimal motion vector can be detected per each area by using a motion vector detecting method suitable for dividing a block into areas with a threshold and a motion vector detecting method suitable for pixel blocks after divided into areas.
The above method can reduce degradation in image quality caused by block distortion. However, even according to the above method, a correct motion vector cannot be obtained in an area with few pixels and a shading (occlusion) area.